U.S. Pat. No. 5,877,187 confers the rights to bilastine, a preparation with antihistaminic properties without sedative or cardiovascular effects. This patent also concerns a procedure to prepare bilastine and the use of this preparation to treat allergic reactions in mammals but it does not include or suggest the possible existence of polymorphic forms of this compound. To prepare pharmaceutical compositions containing bilastine for their administration in mammals and especially in man, in accordance with international health authority specifications, bilastine must be manufactured in the most stable crystalline form possible, especially in a form that has constant physical properties.